Archives For Pati Vitt

Last June, I headed up to Door County, Wisconsin, with Kay Havens, our director of plant science and conservation, for a 31-day trip to undertake our annual fieldwork. “A month at the beach!” you say, thinking it such a treat! Well, yes and no.

Four undergraduate students in our REU program joined us to track literal life and death events in two plant populations on the dunes of Lake Michigan. The dunes can be more than 20 degrees Fahrenheit hotter than ambient temperatures, and we work in the interdunal swales, where no lovely breezes off the lake can reach us. It is often well over 95 degrees in the dunes, even if it’s a balmy 75 degrees in Sturgeon Bay. But, no matter—we are on a mission! On days with the hot sun both beating down and reflecting up from the sand, we observed, measured, and recorded the births, deaths, and reproductive successes of one of our favorite plants: the threatened pitcher’s thistle (Cirsium pitcheri).

Pitcher’s thistle (Cirsium pitcheri)

We find every seedling we can, and place a flag next to it to help us keep track of the ones we’ve counted. We don’t want to miss a single one. Each seedling is a measure of successful reproduction for this monocarpic perennial. Monocarps—plants that only flower once before they die, are completely dependent upon producing as many successful offspring as they can, all in the quest to ensure that they just replace themselves. When all plants successfully replace themselves, a population is stable.

Just to replace yourself is a monumental undertaking for a plant that flowers once and then dies. Especially for pitcher’s thistle. The dunes are a harsh environment for a tiny baby plant. Many of them die—exposed to the heat, and without enough water to sustain them. We estimate that fewer than one in ten seeds germinate and survive each year, and in some years, only a small percent of those survive the winter to become a juvenile plant the next year. That means that each flowering plant must produce many seeds to replace itself. The good news? Generally, if a seedling survives to the juvenile stage, it has a much increased chance of survival to make it to the next stage—a vegetative plant—and the vast majority of those go on to reproduce at some point.

Kay Havens is ready to record data at Ship Canal Nature Preserve, owned by the Door County Land Trust.

However, seed germination and seedling survivorship and growth depend upon two things: where you come from and where you live. To look at this, we took 100 seeds from each of our two study populations and grew them in “seed baskets” in our study garden at the Chicago Botanic Garden. We also grew the same number in seed baskets at their respective home sites. Regardless of population, they germinated and grew very readily in our study garden. But there were very stark differences at our study sites in Door County: seed germination was 39% at one site, but only 9% at the other.

Pitcher’s thistle seedlings sprouted in one of our seed baskets at the Ship Canal Nature Preserve. The pair of yellow-green “leaves” opposite each other are actually cotyledons, or seed leaves, and are the first photosynthetic organs to emerge from the seed during germination.

These are pitcher’s thistle seedlings that have grown very large under the favorable conditions of the test garden on the south side of the Plant Science Center. In just one growing season, they have grown as large as plants three to four years old that grow under natural conditions.

Why the difference? Well, our first site is definitely more hospitable! Even we are happier to work here. It’s not nearly as hot, and the dune structure is more flat, so the breeze off the lake makes things more pleasant—for plants and people alike! And it appears to this observer’s eye that there’s more water available close to the surface here. This year, there are two large patches in the dune that have been perpetually damp. In contrast, our second population is literally high and dry, making life hard for the little pitcher’s thistle seedlings. How does this affect the prospects of these two populations overall? Stay tuned! We’ll let you know when we have finished our analysis of the long-term trends at these two very different sites.

One plant, two places—offering a fascinating glimpse of a life of contrasts.

The standard equipment for the home brewer: a 6-gallon glass “carboy,” a device that fits right on top of the carboy rim called a universal carboy cap, and an air lock.

Although I’m a scientist by trade, I’ve also joined the ranks of home/craft beer makers, and have done a fair bit of brewing myself.

Despite seemingly endless beer varieties, beer making boils down to just a few basic ingredients. So what’s really happening during the major steps in the brewing process? And what do all those colorful beer-making terms mean?

Step 1: Choosing the grain

The basic brewing process begins with grains—generally barley, but also rice, wheat, and/or sorghum. Botanically speaking, grains are grasses with a special type of seed called a caryopsis. Inside a caryopsis is an embryo and a large, starchy food reserve (called the endosperm) that plays a key role in the beer-making process.

Step 2: Making the malt

As a grain seed germinates, its food reserve is converted from starch into smaller carbohydrates. This conversion process is important for the brewer, since those carbohydrates will feed the yeasts during fermentation. The brewer doesn’t want the grain seed to completely germinate, though—if it did, the embryo would “eat” all of the food reserves, leaving none for the yeast.

Instead, grains are only partially germinated, just enough for their starch-converting enzymes to become active. Then the grains are gently heated and dried, so that the enzymes stay active (it’s called diastic power), but the embryo remains inactive. It’s a process known as malting, and its end-product is the key ingredient in most beers: barley malt.

Malted (germinated) barley is used as a base in beer and scotch. Photo via Finlay McWalter, Wikimedia Commons. GFDL

Step 3: Blending the malt

By treating barley malts differently, the brewer can create different colors, flavors, and sweetness levels in their brew. Roasting, for example, affects depth of color and flavor, while using malts with different diastic powers—that ability to convert starch into sugar—affects sweetness. The blending of barleys and barley malts (plus other grains) is part of the art of brewing beer.

Step 4: Mashing the malt

In the process called mashing, malt sugars are extracted from the barley by adding hot water during the starch-converting process. Water dissolves the starches so they leach out of the cracked grain, creating the wort, which is like a syrupy malt tea. Already-prepared malts—and even malt-extract syrups—allow the home brewer to skip the mashing process.

Step 5: Boiling the wort

Home brewers can simply turn up the heat on malt syrup plus hot water to boil the wort—an important step that denatures, or kills, the enzymes that convert starches into sugar. This kills any microorganisms and bacteria in the process, too. Now the art continues, as the brewer can control fermentation and flavor with yeasts and hops.

A beautiful vine for the home garden is hops (Humulus lupulus), pictured here in flower.

Hops add flavor—described from bitter to bright—and can be introduced at the beginning of the boil, midway through, or as finishing hops at boil’s end. Timing plus variety choice (more than 80 varieties of hops are available) determine flavor. Bitter flavor is the result of adding hops at the beginning of the boil, while the characteristic bright, hoppy flavor of India pale ales comes from hops added to the cask after fermentation.

Step 7: Pitching the yeast

Yeast gets added after the wort has cooled sufficiently, in a process called pitching. There are two yeast groups to choose from.

Lager yeasts, which prefer the bottom of the tank, yield Pilsners, Dortmunders, Märzen, Bocks, and American malt liquors, and work happily at 40 degrees F.

Yeasts contribute to flavor, too, creating secondary metabolites such as the phenolics that give German wheat beers their characteristic clovelike flavor. Brewers can experiment with yeasts: California common beers, such as Anchor Steam Ale, were created by adding lager yeasts at ale temperatures (60-70 degrees F.).

Porter, lager, stout, and ale: different malt blends and yeasts create different brews.

Step 8: Fermentation

Fermentation is a preserving process known since Neolithic times: beer, wine, pickles, sauerkraut, and hot pepper sauces are all fermented. Yeasts cause fermentation by converting the sugar in the wort to alcohol. When yeasts—either dry or liquid—are pitched into a well-aerated wort, a controlled population explosion occurs. Yeasts suddenly go into metabolic overtime, reproducing at a rapid rate. Fermentation begins as sugars are consumed. The amount of sugar in the wort, the temperature at fermentation, and the type of yeast pitched determine the metabolic byproducts: alcohol and CO2.

Step 9: Conditioning

Fermentation is a two-stage process. Primary fermentation occurs after the controlled population explosion, and begins to subside, or attenuate, as the alcohol content increases. Alcohol rises to the top of the fermentation tank, while most of the yeasts fall to the bottom and become inactive. (Some do not.) Most brewers transfer the wort to a secondary fermentation tank at this point; the second fermentation occurs more slowly, and conditions the beer as the more complex sugars are converted. Once the beer is fully conditioned, it’s bottled or transferred to a cask or keg.

Think about the science next time you speak the language of beer and order a light, crisp, transparent American lager…a rich, creamy, almost-opaque stout…or something in between.

And which kind of beer most appeals to me? I often have trouble choosing between a bright, crisp India pale ale such as Sierra Nevada, or something a lot darker, like a Guinness. I guess I’m just a fan-atic!